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Substrate specificity in glycoside hydrolase family 10: Tyrosine 87 and leucine 314 play a pivotal role in discriminating between glucose and xylose binding in the proximal active site of pseudomonas cellulosa xylanase 10A

Lookup NU author(s): Simon Andrews, Professor Jeremy Lakey, Professor Harry Gilbert

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Abstract

The Pseudomonas family 10 xylanase, Xyl10A, hydrolyzes β1,4-linked xylans but exhibits very low activity against aryl-β-cellobiosides. The family 10 enzyme, Cex, from Cellulomonas fimi, hydrolyzes aryl-β-cellobiosides more efficiently than does Xyl10A, and the movements of two residues in the -1 and -2 subsites are implicated in this relaxed substrate specificity (Notenboom, V., Birsan, C., Warren, R. A. J., Withers, S. G., and Rose, D. R. (1998) Biochemistry 37, 4751-4758). The three-dimensional structure of Xyl10A suggests that Tyr-87 reduces the affinity of the enzyme for glucose-derived substrates by steric hindrance with the C6-OH in the -2 subsite of the enzyme. Furthermore, Leu-314 impedes the movement of Trp-313 that is necessary to accommodate glucose-derived substrates in the -1 subsite. We have evaluated the catalytic activities of the mutants Y87A, Y87F, L314A, L314A/Y87F, and W313A of Xyl10A. Mutations to Tyr-87 increased and decreased the catalytic efficiency against 4-nitrophenyl-β-cellobioside and 4-nitrophenyl-β-xylobioside, respectively. The L314A mutation caused a 200-fold decrease in 4-nitrophenyl-β-xylobioside activity but did not significantly reduce 4-nitrophenyl-β-cellobioside hydrolysis. The mutation L314A/Y87A gave a 6500-fold improvement in the hydrolysis of glucose-derived substrates compared with xylose-derived equivalents. These data show that substantial improvements in the ability of Xyl10A to accommodate the C6-OH of glucose-derived substrates are achieved when steric hindrance is removed.


Publication metadata

Author(s): Andrews SR; Lakey JH; Gilbert HJ; Charnock SJ; Davies GJ; Claeyssens M; Nerinckx W; Underwood M; Sinnott ML; Warren RAJ

Publication type: Article

Publication status: Published

Journal: Journal of Biological Chemistry

Year: 2000

Volume: 275

Issue: 30

Pages: 23027-23033

ISSN (print): 0021-9258

ISSN (electronic): 1083-351X

Publisher: American Society for Biochemistry and Molecular Biology

URL: http://dx.doi.org/10.1074/jbc.M000128200

DOI: 10.1074/jbc.M000128200

PubMed id: 10767281


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